Bubble Nucleation from Boson Star Collapse

Abstract

We present a new classical mechanism for nucleation of bubbles of true vacuum. The mechanism arises when dense boson stars form in the false vacuum. As the boson stars collapse due to attractive self-interactions, the field inside the stars core is enhanced beyond the potential barrier. Subsequently the stars explode as true vacuum bubbles, and induce a cosmological phase transition. The mechanism raises the possibility that a vacuum that is stable against quantum tunneling can be vulnerable to ``astrophysical'' processes.

Figures (4)

• Figure 1: $\tilde{\rho}\equiv \tilde{\phi}^2+\dot{\tilde{\phi}}^2$ at the center of the star ($\tilde{r} = 0$), as a function of time. The numerical results are shown by the solid lines, whose colors denote different values of the sextic coupling $\delta$. The origin of time is chosen such that $\tilde{t} = 0$ corresponds to the moment when the self-similar attractor (\ref{['eq:axistar-collapse']}), shown as the red dashed line, becomes singular. The sub-panel shows a zoom-in of the region around $\tilde{t} = 0$. For the green line ($\delta = 0.625$) the vacua are degenerate. For $\delta \lesssim 0.37$, the field becomes stabilized in the true vacuum and a phase transition is triggered. All quantities are in dimensionless units defined in (\ref{['eq:d-less']}).
• Figure 2: Snapshots of the radial profile of $\tilde{\rho}$. The line colors denote different times, as indicated by the tick values in the legends. The red dashed line shows the self-similar profile (\ref{['eq:axistar-collapse']}) at $\tilde{t} = -1$. ($\tilde{t} = 0$ is when the self-similar profile develops a central singularity.) The sextic coupling $\delta$ is varied in the two panels. In both panels the star core initially undergoes a self-similar collapse. In the upper panel a supercritical bubble forms in the core, and begins to expand. In the lower panel a subcritical bubble forms, whose central field value turns to decrease as outgoing waves are emitted. All quantities are in dimensionless units defined in (\ref{['eq:d-less']}).
• Figure 3: Profiles of bounce solutions for various values of the coupling $\delta$. The red dashed line shows the self-similar profile (\ref{['eq:axistar-collapse']}) in the limit $\tilde{t} \to 0^-$. The rough condition (\ref{['eq:cond-gener']}) for supercriticality is satisfied for $\delta \lesssim 0.2$. All quantities are in dimensionless units defined in (\ref{['eq:d-less']}).
• Figure 4: Parameter space where phase transitions can happen, in terms of the couplings $\delta$ and $\lambda$ for the sextic model. Below black lines the universe is stable against quantum tunneling up to today, with the mass of $\phi$ varied as $m = 1\, \mathrm{GeV}$ (dashed), $10^2\, \mathrm{GeV}$ (dotted), $10^4\, \mathrm{GeV}$ (dot-dashed), and $10^6\, \mathrm{GeV}$ (solid). In the red shaded area phase transitions can happen due to the boson star collapse.